The present invention relates to the cleaning of wafers. More specifically, the present invention relates to an apparatus and method for the cleaning of wafers post-chemical mechanical planarization (post-CMP) processing using a pencil stylus-like brushcleaner.
Chemical mechanical polishing (CMP) is one of the methods to planarize the patterned semiconductor surfaces, and is also called chemical mechanical planarization. It is the most noticeable technology in the current integrated circuit (IC) process, and is also a key technology for future micro processing. The purpose of this technology is to planarize the dielectric layer or the metal layer on a wafer. In accordance with the design of IC devices toward small size and with multiple layer interconnections, lithography process has a higher limitation on the depth of focus (DOF), and thus has extremely high requirements for the planarization technology. This technology has become even more important for CPU and LOGIC products that have more than three metal layers. Since the polishing process requires that the slurry used have some chemical effect on the wafer surfaces in addition to simply mechanical polishing, this technology is thus named chemical mechanical polishing/planarization. It cannot only reduce the inferior rate of the device products, but also has considerable contribution in the improvement of product reliability.
To improve microprocessor and memory cost/performance ratios as well as increasing factory productivity in semiconductor chip production, manufacturers are finding ways to reduce chip size and add more levels of interconnect wiring. As product design rules are reduced from 0.5 xcexcm to 0.35 xcexcm and to 0.25 xcexcm, lithographic depth of focus (DOF) shrinks from 2.0 xcexcm to 1.0 xcexcm to 0.8 xcexcm. To obtain the largest process window with step and repeat lithography equipment, the entire wafer must be at optimum focus during the exposure. Thus, surfaces must be planar. Consequently, most process development for 0.35 xcexcm DRAMs or microprocessors requiring more than two levels of metal is incorporating planarization technology.
The residues produced by CMP must be removed prior to subsequent wafer processing, and the removal technique must not be damaging to the wafer. Water washing alone, or brushcleaning with deionized (DI) water is not sufficient for removing residual contaminants. A separate post-CMP cleaning step is required for removal of chemicals and slurry particles from the wafer. This step is typically achieved by mechanical brush cleaning, using a polyvinyl alcohol (PVA) brush or sponge and DI water, or potassium or ammonium hydroxide as the cleaning agent.
A growing number of CMP tools have integrated cleaners and several types of wafer cleaning are utilized at various points in the above-described processes. The type of cleaning process chosen depends on the surfaces being cleaned, and the contaminant(s) being removed (e.g., particulates or film residues such as solvent or photoresist developer residues or metallic films deposited during immersion etching). Ultrasonic scrubbing or mechanical scrubbing can remove insoluble particles. Mechanical scrubbing can be accomplished by a combination of high pressure DI water spraying and brush scrubbing (wherein the rotating PVA sponge or bristle brush makes contact or hydroplanes over the wafer surface).
One problem encountered in polishing or cleaning processes is the non-uniform removal of the semiconductor surface. Removal rate is directly proportional to downward pressure on the wafer, rotational speeds of the platen and wafer, slurry particle density and size, slurry composition, and the effective area of contact between the polishing pad and the wafer surface.
Conventional systems lack control of sponge compression or the pressure applied by a sponge to a wafer when cleaning a wafer post-CMP processing without altering the vertical travel of the arm assembly. In addition, when the conventional scrubbing equipment performs cleaning on wafers the distance between the brush and wafer and, therefore, brush pressure is varied across the wafer due to runout (wobble) of the rotary chuck holding the wafer. Therefore, the conventional scrubbing equipment may damage the semiconductor wafer being cleaned and cannot ensure the effectiveness of cleaning, and time is wasted during each readjustment to obtain the same pressure across the wafer. There thus remains a need for an improved method and apparatus to provide post-CMP cleaning with a sponge maintaining constant pressure independent of the vertical height of an arm assembly that controls a cleaning head in contact with a wafer surface and independent of various mechanical influences of the tool itself. There further remains a need for an apparatus and method that allows for the changing of sponges while maintaining the same pressure on a wafer without readjustment of the arm assembly, as well as the ability to vary the amount of pressure applied to the wafer if so desired.
The above-described circumstances are overcome and alleviated by the present apparatus and method for cleaning of a semiconductor wafer. The apparatus and method allow for uniform cleaning pressure, which is applied to a wafer by a cleaning sponge, so as to uniformly clean the entire surface of the wafer and also allow for varying the pressure applied, as well as sponge replacement, in a simple manner.
A wafer cleaning apparatus for biasing a cleaning agent with a constant force against a wafer to clean a surface of the wafer, the wafer cleaning apparatus comprising: a carrier for sustaining the wafer against the cleaning agent; a liquid supply for furnishing liquid to the surface of the wafer for cleaning; an end effector holding the cleaning agent and the cleaning agent having a bias towards the wafer; and an arm assembly and a shaft capable of supporting the end effector.